1. Field of the Invention
The present invention relates to a system and method for operating as an induction motor or a stepping motor, and more particularly, to a system and method that simulates the characteristics of the induction motor under the configuration of the stepping motor.
The present invention also relates to a system and method for providing a speed control switched between high/low rotational speed that is adapted to a scanner for scanning a sheet under a stepping mode and for previewing or flying back the scan carriage under an induction mode.
2. Description of the Prior Art
The advancement of the electric engineering brings the modern computers to serve people with more functions through the aids of the peripheral devices. For example, users may perform further image processing in their computers on those images generated by scanning photos or sheets through scanners after the images being stored in an image format. Conventionally, scanners usually employ stepping motors for providing dynamics for controlling scan operations because of the characteristics of low rotational speed and high rotational distance, which makes the stepping motors adapted to scanners for controlling the moving operations of the scan lines.
It is also an important issue for the persons skilled in the scanners to reduce the scan time for preview except to promote scan resolutions or to make the scanner steady and smaller. Different scan regions are usually denoted by different marks and in accompanied with the operations of scanning the marks before scanning photos or sheets. However, dynamics for control the preview operations are also provided by the stepping motors mounted in the conventional scanners, which indicates that the preview operations can not be further simplified because of low rotational speed. On the other hand, a higher scan speed may be employed for those low, resolution applications because a low resolution image usually consists of less scan lines than a high resolution image. Moreover, when the scan carriage that is used for scanning the photos or sheets flies back, there only have to move the scan carriage back to its original without any scan operations, which indicates that the operation time can be furthermore decreased.
Nevertheless, although both the DC motors and induction motors have the characteristics of high rotational speed, the lives of the DC motors usually concerned with switch brushes and the induction motors usually need a larger torque while starting. A single dynamics is usually provided by stepping motors for all operations in conventional scanners due to cost consideration. It is difficult to mount more than one motor in a scanner to respectively upgrade the performances of the above two approaches without increasing the manufacture cost.
The principal object of the present invention is the provision of a motor combination system and method that operates as an induction motor or a stepping motor through a switch mechanism.
The other object of the invention is the provision of a motor combination system and method that performs as an induction motor under a configuration of the stepping motor.
A further object of the invention is the provision of a motor combination system and method that provides different rotational speeds for the applications that require a control switch between high/low rotational speeds.
A still further object of the invention is the provision of a motor combination system and method that provides a switch control between high/low rotational speeds for employing in the applications that require different performance speeds.
The disclosed system basically encompasses a switch device, an induction motor control module, and a stepping motor control module, wherein driving signals generated by the above two modules are directed to the switch device for motor rotation controls. The induction motor control module further receives feedback signals indicative of the instantaneous rotation speed of the motor to compensate for rotation distortions when the motor operates under an induction mode. The switch device is under controlled by a mode selection signal for selecting the driving signal from one of the above two modules for achieving the purpose of controlling motor rotations.
In one embodiment, the induction motor control module encompasses an encoder, a phase detector, a distortion evaluating device, a microprocessor, and a pulse width modulator (PWM). The encoder detects and then encodes the instantaneous conditions of the motor rotations. The phase detector decodes the encoded conditions from the encoder before routing to the distortion evaluating device. The distortion evaluating device compares the decoded instantaneous rotation conditions with an induction signal provided for an actual induction motor to derive a distortion evaluation of the motor rotations. A microprocessor is responsive to the distortion evaluation to generate a waveform adjustment control signal employed for regulating pulse width of the PWM for controlling the motor to go forward or backward. The AC driving circuit is then responsive to the signal output from the PWM for generating the driving signal for feeding into the switch device. In one embodiment, the stepping motor control module basically encompasses a stepping motor driving circuit for generating the driving signal for operating under in the stepping mode and for feeding to the switch device. The switch device is responsive to a detect result associated with the torque and a mode selection signal to switch the motor to operate between the induction and stepping modes.
In the disclosed method, the motor operates under the stepping mode to provide torque for operations. When the torque is large enough, the switch device can switch the motor to operate under the induction mode or to continue in the stepping mode according to the indication of the mode selection signal.